Riots that swept across the UK were the result of a penal system that fails to stop "a feral underclass" reoffending, the Justice Secretary has said.

Riots that swept across England were the result of a penal system that fails to stop "a feral underclass" reoffending, the Justice Secretary has said.

Writing in The Guardian, Kenneth Clarke revealed that 75% of over-18s charged with involvement in last month's unrest had criminal records.

In brief excerpts on the newspaper's website, he claimed that the "broken penal system" had failed to stop the "criminal classes" from reoffending.

He said that there was "a feral underclass, cut off from the mainstream in everything but its materialism".

Mr Clarke said sentencing for offenders had been "about right", but added: "In my view, the riots can be seen in part as an outburst of outrageous behaviour by the criminal classes - individuals and families familiar with the justice system, who haven't been changed by their past punishments."

He called for Government action to tackle "an appalling social deficit" revealed by August's unrest.

The Home Affairs Select Committee will today hear evidence on the wave of violence and theft from witnesses including Mayor of London Boris Johnson and senior Met officers such as Acting Commissioner Tim Godwin.

Mr Clarke's outspoken comments came as a new study to examine the causes and effects of last month's disorder was launched.

Reading The Riots, compiled by The Guardian and the London School of Economics, will include surveys of those who took part in the disorder and interviews with residents, police and the judiciary.The report will also analyse two databases put together by the newspaper, which contain more than 2.5 million riot-related Twitter messages and statistics about more than 1,000 defendants who have appeared in court charged with riot-related offences.

Senior politicians and legal figures have expressed widely differing opinions about appropriate punishments for those involved in the violent unrest and looting.

On Friday Director of Public Prosecutions Keir Starmer warned that they should be treated in the same way as other offenders.

Concerns have been raised that some of the sentences handed down were too tough, for example two men accused of trying to incite unrest via Facebook were each jailed for four years.

Mr Starmer said: "We should not treat these cases as a separate category to be dealt with differently."We should treat them as we do any other case. We need to keep our feet on the ground."

However Prime Minister David Cameron has praised the "tough message" that the courts have been handing out.

Recent figures released by the Ministry of Justice (MoJ) show more than 1,500 people have now appeared in court over the riots, in which five people died across the country.

One in five (22%) of those before the courts were youths, aged 10 to 17, and nine in 10 (91%) were male.

Two in three have been remanded in custody, compared with an average of one in 10 who were charged with serious offences in 2010. The remaining 443 have been granted bail, the MoJ figures showed.

Most of the charges (1,027) have been made in the capital, while 190 have appeared before courts in Greater Manchester, 132 in the West Midlands, 67 in Merseyside and 64 in Nottingham.

The Metropolitan Police Authority said the disturbances will cost the force more than £34 million, with the total expected to rise even further as the final bills from other forces called in to help are settled.